The above-described semiconductor device is manufactured according to a following method. Firstly, an assembly including the semiconductor element and the pair of metal plates is prepared. Next, the assembly is set in a cavity of a mold configured to form the resin package. In the cavity, one metal plate of the pair of metal plates is in contact with a bottom surface of the cavity and the other metal plate of the pair of metal plates is in contact with an upper surface of the cavity. When resin is injected into the cavity, the assembly interposed between the bottom surface and the upper surface of the cavity thermally expands, and the semiconductor element interposed between the pair of metal plates may be damaged by being pressed. Therefore, the assembly is set in a state where one metal plate of the pair of metal plates is in contact with the bottom surface of the cavity and a space is ensured above the other metal plate of the pair of metal plates. Then, the cavity is filled with molten resin. The space above the other metal plate is also filled with the molten resin in the cavity. The other metal plate expands upward, and thus the semiconductor element is not pressed.
Solidified resin (the resin package) is extracted from the mold. The one metal plate which was in contact with the bottom surface of the cavity is exposed at the resin package, whereas the other metal plate is covered with the resin. Then, a surface of the resin package is removed to expose the other metal plate. Such a manufacturing method is described, for example, in Japanese Patent Application Publication No. 2007-73583 and in Japanese Patent Application Publication No. 2009-302281.